1. Field of the Invention
The present invention relates to a high-density circuit module used in various electronic apparatuses, e.g., a high-density circuit module providing a front end of a broadcasting radio receiver and to a process for producing the high-density circuit module.
Such a front end of a broadcasting radio receiver comprises a high-frequency amplifying circuit, tuning circuit, locally oscillating circuit, mixing circuit, intermediate-frequency amplifying circuit, etc. In particular, the front end of the broadcasting radio receiver is made with a small high-density circuit module in which circuit components, e.g., a chip resistor, chip capacitor, semiconductor device and coil are soldered to a printed wiring board covered with a shielding plate. The present invention is directed to the above-mentioned high-density circuit module and the process therefor.
2. Description of the Prior Art
FIGS. 1A, to 1K illustrate a process of producing a conventional high-density circuit module. In FIG. 1A, 41 denotes a printed wiring board. The top surface of the printed wiring board 41 has a topside conductor pattern (not shown) formed thereon and electrically connecting various electronic components mounted on the printed wiring board. The underside surface of the printed wiring board 41 has a shielding conductor pattern (not shown) formed thereon. 42 denotes a creamy solder applied by printing, dispensation etc. to the top surface of the printed wiring board 41. As shown in FIG. 1B, 43 denotes a chip resistor 43 the opposite ends of which have connection terminals 43a and 43b. Resistor 43 is mounted on the printed wiring board 41 so that the connection terminals 43a and 43b are in contact with the creamy solder 42 provided on the printed wiring board 41. As shown in FIG. 1C, by reflowing the solder 42 applied to the printed wiring board 41 on which the chip resistor 43 is mounted, the conductor pattern of the printed wiring board 41 is connected by means of soldering 44a to the connection terminals 43a and 43b of the chip resistor 43. As shown in FIG. 1D, 46 denotes a tie bar in the form of a thin metal strip wherein a plurality of external leads 45a and a plurality of retaining pieces 45b are integrally formed to the tie bar 46. As shown in FIG. 1C, one side of the printed wiring board 41 is inserted between the plurality of external leads 45a and the plurality of retaining pieces 45b. As shown in FIG. 1E, then the front end of each of the external leads 45a is connected by means of soldering 44b to the topside conductor pattern of the printed wiring board 41. As shown in FIG. 1F, then a framework 47 made of a metal plate covers the printed wiring board 41. As shown in FIG. 1G, then the framework 47 is fastened by soldering 44c to the printed wiring board 41. As shown in FIG. 1H, then an upper shielding case 48 is mounted an the top edge of the framework 47. As shown in FIG. 1I, then a lower shielding case 49 is mounted to the bottom surface of the framework 47. As shown in FIG. 1J, then the upper and lower shielding cases 48 and 49 are fastened by solderings 44d to the framework 47. As shown in FIG. 1K, the tie bar 46 is finally cut off the external leads 45 so that the prior-art high-density circuit module is completed. By soldering the external leads 45a of the complete high-density circuit module to a main printed wiring board (not shown) an electric circuit of the high-density circuit module is electrically connected to an electric circuit of the main printed wiring board by means of the external leads 45a. FIGS. 1A to 1K illustrate a single chip resistor 43 of a plurality of circuit components mounted on the printed wiring board 41. However, a number of circuit components are actually mounted on the printed wiring board 41.
Thus, the prior-art process of producing the high-density circuit module comprises the eleven steps of FIGS. 1A to 1K. This prior-art process requires a large number of parts and a large number of steps, so that a material cost and processing cost are increased.